Metallic can bodies, typically formed of aluminum or steel alloys, are now routinely formed by drawing and ironing a circular blank of sheet metal into a cylindrical can body.
Especially in the case of aluminum alloy can bodies, in which the thinned side walls provide insufficient structural strength for the can, the can bottom closing structure is of vital importance to can quality. There are numerous patents in the literature concerning bottom structures for can bodies.
The bottom structure of the can body is formed at the end of the draw and iron cycle. A punch carrying the can body through the draw and iron dies includes at the end thereof a die structure corresponding to the bottom structure to be formed in the can bottom. At the end of the stroke carrying the can body through the press, the can bottom and punch strike against a bottom former. This bottom former also includes die structure which, with the die structure of the punch, forms the bottom structure in the can body. The bottom former plug is mounted so as to provide a resilient, yet firm, pressure between the can body and the bottom former at their point of contact.
Traditionally, bottom former have been mounted to provide resilient force by mounting either against a rubber back-up pad or against a pneumatic pressure cylinder. However, the recent advent of substantially increased diameter draw and iron can bodies has resulted in a need for higher pressure levels between the bottom former and the punch in order to successfully form bottom structures on these larger cans without wrinkling of the metal in the can.
It is thus the primary objective of the present invention to provide a bottom former for a draw and iron can-making press which provides increased force against the can body and punch when the can body and punch contact the bottom former, while maintaining a resiliency in the bottom former.